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C. EYZAGUIRRE 



potential. In Fig. 14 (upper portion) a relaxed fast-adapting cell had a resting 

 potential of about 60-70 mV. By appropriate stretch this potential was 

 reduced by 16-5 mV to a new maintained level when the inhibitory nerve 

 fiber was excited at 20/sec. Each inhibitory impulse, in this illustration, 

 caused a repolarization of 9-7 mV which was rapidly attained and then 

 decayed almost entirely within 50 msec. If a cell was held under less stretch, 

 and therefore was less depolarized, the inhibitory potential became progres- 

 sively smaller. When the cell was relaxed to about 6 mV above its own 

 membrane potential each inhibitory impulse set up a small initial depolariza- 

 tion followed by a polarization phase. Figure 14 (upper portion) shows the 



Fig. 14. (Upper portion) — Effect of inhibitory impulses at different membrane 

 potential levels, intracellular leading. Fast receptor cell of second abdominal 

 segment. Trains of inhibitory impulses at 20/sec. a. Cell stretched causing 

 initial maintained depolarization of 16-5 mV. Inhibitory impulse repolarization 

 peaks 9-7 mV. b and c. During progressively lower stretch and higher membrane 

 potential levels the same train of impulses sets up smaller inhibitory potentials of 4 

 and 1 mV. d. Still further relaxation of stretch. Inhibitory impulse sign reverses. 

 Initial depolarization follows each inhibitory stimulus. {Lower portion) — 

 Inhibitory potentials at different levels of stretch. Fast cell. Intracellular records. 

 A. Receptor almost completely relaxed, six inhibitory impulses at 30/sec 

 caused depolarization potentials (arrows). At third arrow stretch causes about 

 20 mV depolarization and three discharges followed by inhibitory train setting 

 up repolarization potentials. Further continued increasing stretch results in 

 afferent impulses which gradually decline in height. At gap 10 sec of record cut 

 out. In B, same inhibitory train; the repolarization potential reaching 12 mV. 

 c. During complete relaxation of cell 6-5 mV inhibitory depolarization peaks 

 are seen (From Kuffler and Eyzaguirre, J. Gen. Physiol. 39 : 155-184, 1955.) 



